1. Field of the Invention
The present invention relates to explosive blasting techniques and more particularly, but not by way of limitation, to the use of multiple detonation points in a long chain of explosives to reduce burn time and the use of an air gap method and apparatus to reduce the quantity of explosive materials.
2. History of the Prior Art
In the practice of standard blasting methods, elongated boreholes are drilled into a rock formation which is to be removed. The borehole is then completely filled with explosives including solid, liquid or gelatin chemical compounds, which upon detonation, are converted to intensely hot gaseous compounds that, because of confinement within the borehole, exert tremendous destructive forces against the confining rock which typically yields to these forces and is reduced to a rubble which can be further processed by mechanical equipment.
An example of a widely used chemical mixture is ammonium nitrate mixed with a carbonaceous material such as diesel fuel. This mixture, when rapidly brought to a critical temperature and pressure by the detonation of a small primer charge, explodes to form a gaseous mixture of nitrogen, carbon dioxide and water vapor expressed by the equation, EQU 3NH.sub.4 NO.sub.3 +CH.sub.2 .fwdarw.CO.sub.2 +3N.sub.2 +7H.sub.2 O.
The use of this or any other explosive compound or mixture entails replacing the air in a borehole as the hole is partially or entirely filled with the solid, liquid or gelatin compound. The explosive upon detonation is essentially converted to gaseous products similar to the air which has been replaced.
A chronic problem associated with blasting for the purpose of fragmenting rocks is the creation of seismic disturbance of the surrounding area which occasionally results in structural damage to buildings, roadways and even mining equipment at or near the site of the blast. The creation of dust fog, flying projectiles and the shattering effect of high amplitude sound waves have always plagued blasting operations in mining and construction projects.
The seismic shock problems are greater when the blast is large and the explosive charge may become quite large when utilizing boreholes of considerable length. The utilization of long boreholes and hence, large charges of explosives is often dictated by production schedules and hence, the safety of such operations is sometimes compromised for economic expediency.
Although technological advancement has provided more stable and effective explosive chemicals, the advance in blasting techniques has been slow and tedious and the foregoing problems have, for the most part, been left unsolved.